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Human activities have been seriously damaging the world's coral reefs for longer than previously thought, and most may not survive more than a few decades, a series of new international studies has concluded.

In a gloomy tally of the status of global coral reef systems, several teams of researchers have concluded that none are left in pristine condition, some 30% are already severely damaged and almost 60% may be lost by 2030, according to several reports published jointly today by scores of scientists in the journal Science.

Human impacts had put reefs in serious trouble even before the recent mass die-offs caused by disease and bleaching, said one team led by Dr John Pandolfi, a paleobiologist at the National Museum of Natural History in Washington.

"Coral reefs and associated tropical near-shore ecosystems have suffered massive, long-term decline in abundance, diversity, and habitat structure due to overfishing and pollution," he said.

Using a wide variety of evidence - including fossils, archaeological sites, coral cores and fishing records - the team reconstructed the ecological histories of 14 coral reefs around the world. They found that these had been degrading for at least two centuries, and that the recent die-offs could spell their imminent demise.

It found that the average ecological status of each of seven 'guilds' - the species that occupy a similar niche in an ecosystem - of animals and plants declined sharply over time: "In general, large animals declined faster than small animals and free-living animals declined more rapidly than architectural builders, such as seagrasses and corals.

"Large carnivores and herbivores were almost nowhere pristine by the beginning of the 20th century, when these guilds were already depleted or rare in more than 80 per cent of the 14 regions examined," Pandolfi and his team found.

Reefs in the western Atlantic have declined more severely than in Australia or the Red Sea. Although the best-protected reefs in the world, on the Great Barrier Reef, are the closest to pristine, they are also one-quarter to one-third of the way along the path to ecological extinction.

The reefs of Moreton Bay, at the extreme southern end of the Great Barrier Reef, "are as close to ecological extinction for all seven guilds as the severely degraded reefs of eastern Panama and the Virgin Islands," the researchers said.

Great Barrier Reef in decline

"Most importantly from the perspective of reef conservation and management, most of the reef ecosystems were substantially degraded before 1900," they continued. "Recent widespread and catastrophic episodes of coral bleaching and disease have distracted attention from the chronic and severe historical decline of reef ecosystems."

They argue that the evidence suggests that maintaining the status quo will not be enough to save coral reefs: "Regardless of the severity of increasing threats from pollution, disease, and coral bleaching, our results demonstrate that coral reef ecosystems will not survive for more than a few decades unless they are promptly and massively protected from human exploitation."

Extinctions likely

A second team led by Professor Terry Hughes, of the Centre for Coral Reef Biodiversity at James Cook University in Townsville, said that projected global increases in carbon dioxide and temperature over the next 50 years will exceed the conditions under which coral reefs have flourished over the past half million years.

"Coral reefs are highly productive hotspots of biodiversity that support social and economic development," he said. "Their protection, therefore, is a socio-economic imperative, as well as an environmental one."

The scientific paper predicts that reefs will change rather than disappear entirely: "On many reefs, reduced stocks of herbivorous fishes and added nutrients from land-based activities have caused ecological shifts, from the original dominance by corals to a preponderance of fleshy seaweed."

Hughes and colleagues said that management strategies need to be designed and implemented through international, co-operative efforts because reefs do not observe human borders. Protected reef sanctuaries, called 'no-take areas', must be vastly expanded to support reef resilience and to provide a safe place for the breeding of the fish and other creatures that are crucial to coral reef ecosystems, they said.

Ecological modelling studies indicate that at least 30% of the world's coral reefs should be no-take areas to ensure long-term protection and maximum sustainable yield of exploited stocks: "Yet, even in affluent countries, such as the United States and Australia, less than 5% of reefs today are no-take areas," the scientists note.

Reef sanctuaries not enough

It cautions, however, that protective zoning does do not prevent or hold back warm water, or stop bleaching. In 1998, the biggest and most destructive bleaching event to date killed an estimated 16% of the world's corals, including reefs in the western Pacific, Australia, and Indian Ocean that are widely regarded as the best managed and healthiest in the world.

"Local successes at protecting coral reefs over the past 30 years have failed to reverse regional-scale declines, and global management of reefs must undergo a radical change in emphasis and implementation if it is to make a real difference," the researchers said.

Growing human populations and improved storage and transport systems have exponentially increased historic human impacts on reefs, with markets for fishes and other natural resources becoming global and reef resources are now supplied to places far removed from the tropics.

Climate change will compound these problems and accelerate the rate of decline, they forecast: "The link between increased greenhouse gases, climate change, and regional-scale bleaching of corals, considered dubious by many reef researchers only 10 to 20 years ago, is now incontrovertible.

"Moreover, future changes in ocean chemistry due to higher atmospheric carbon dioxide may cause weakening of coral skeletons and reduce the accretion of reefs, especially at higher latitudes. The frequency and intensity of hurricanes (tropical cyclones, typhoons) may also increase in some regions, leading to a shorter time for recovery between recurrences," they said.

Changes too fast for reefs

"A major concern is that the accelerating rate of environmental change could exceed the evolutionary capacity of coral and zooxanthellae [algae that live symbiotically with coral] species to adapt. A common view is that corals are too long-lived to evolve quickly, and that geographic differences in temperature tolerances have evolved over much longer time frames than the decadal scale of current changes in climate."

A third team led by Nerilie Abram of the Australian National University in Canberra, has concluded that the huge wildfires that burned large tracts of tropical forest in Indonesia in 1997 may have indirectly led to the suffocation and death of almost all of the coral and fish in the Mentawai Islands reef ecosystem.

The fires released an estimated 11,000 tonnes of iron into the atmosphere, which settled on the ocean surface and apparently prompted a massive 'red-tide' algal bloom that smothered the reef system.

Another team led by Dr Toby Gardner of the University of East Anglia in Britain, reports that a massive region-wide decline of corals has occurred across the entire Caribbean basin, with the average hard coral cover on reefs being reduced by 80% in three decades.